In EP-A-0,163,424 thin films made from polyethylene of ultrahigh molecular weight and a process for their production are described. This process consists of dissolving polyethylene of ultrahigh molecular weight in a solvent, shaping the solution into a tape, cooling the tape to a temperature below the gelation temperature, a gelled tape being formed, partly removing the solvent from the gelled tape, the gelled tape being fixed in the longitudinal and transverse directions, heating the gelled tape and stretching biaxially in the usual manner.
Since the thin films obtained in this manner exhibit pores and therefore are cloudy, they are subjected to a compression process at a temperature below the melting point of the polyethylene, a press or calendar being used.
This compression treatment is not able however to remove all pores and represents a measure which makes a continuous production of film on an